As with previous articles on this topic we start with the geology. The shape and structure of the land is informed by its geological history and then what has happened in the intervening thousands of years. The geology of Mull is not for the faint-hearted; it has been described as "...the most complicated igneous centre as yet accorded detailed examination anywhere in the world..." Geological Survey of Scotland 1924.

Mull is 24 miles (N-S) by 26 miles (E-W) but the shape is complicated by the deeply indented sea lochs which, in the waist, cut the island coast-to-coast distance down to around eight miles. The hugely layered volcanic structure, with up to 20 stacked-up lava flows make for undulating and twisting roads and progress in any direction, by any mode of transport, is slow (and rewarding!). Almost every mile of road is single track with just a couple of stretches of two-way traffic in a couple of towns. By way of example, the route from Tobermory to Dervaig is a twisting snake, full of hidden summits and switch-backs. It takes around 45 minutes to over the eight miles in a camper van (or the local bus) and the section record for the Mull Car Rally is an amazing 8 minutes or so (at night!).